I thought it was going to one of the lightest 700's, so a massive power system was not going to be needed.
Having said that, I will still stick the biggest motor I can fit into it for extreme performance

I'm sure there will be a barebones kit so you can choose what ever motor you like for it. A Pyro 700 with 4000mAh packs would probably make the lightest setup. Or if you want you could use up the weight allowance on bigger packs, say 6000mAh and get longer flight times. No setup is ideal for everyone but if the airframe is very light then there is flexibility for everyone. Unlike some machines that are so heavy they need an overkill powersystem, which make it even more heavy and flight times even shorter.

I just want to know if a 160Amp esc is needed since the belt creates excessive drag.

No you will probably find that overall the Protos 700 uses less power than most other 700's. The biggest problem to solve is gear ratios. To use the same KV motors in an all belt system you need a massive main gear.

In fact, a belt actually has less drag at high speed, since the belt is pulled away from the pulley by the rotation.

+1. The centrifugal force on the belt reduced the friction against the cogged pulleys to almost nothing, while at the same time throwing the belt against the idler pulleys, securing it in place. The system is beautiful in its simplicity.